Terrestrial Planet Evolution in the Stagnant-Lid Regime: Size Effects and the Formation of Self-Destabilizing Crust

TL;DR

This study uses thermal evolution simulations to explore how planetary size influences crust and mantle dynamics in stagnant-lid planets, revealing size effects, the role of lithosphere hydration, and potential for self-destabilizing crust formation.

Contribution

It provides the first systematic analysis of size effects on terrestrial planet evolution in the stagnant-lid regime, incorporating rheology, phase transitions, and crustal processes.

Findings

Crustal thickness decreases with planetary mass.

Lithosphere hydration dominates size effects on evolution.

Massive planets may develop self-destabilizing eclogite layers.

Abstract

The ongoing discovery of terrestrial exoplanets accentuates the importance of studying planetary evolution for a wide range of initial conditions. We perform thermal evolution simulations for generic terrestrial planets with masses ranging from that of Mars to 10 Earth-masses in the stagnant-lid regime, the most natural mode of convection with strongly temperature- dependent viscosity. Given considerable uncertainty surrounding the dependency of mantle rheology on pressure, we choose to focus on the end-member case of pressure-independent potential viscosity, where viscosity does not change with depth along an adiabatic temperature gradient. We employ principal component analysis and linear regression to capture the first-order systematics of possible evolutionary scenarios from a large number of simulation runs. With increased planetary mass, crustal thickness and the degree of mantle processing are both predicted to decrease, and such size effects can also be derived with simple scaling analyses. The likelihood of plate tectonics is quantified using a mantle rheology that takes into account both ductile and brittle deformation mechanisms. Confirming earlier scaling analyses, the effects of lithosphere hydration dominate the effects of planetary mass. The possibility of basalt-eclogite phase transition in the planetary crust is found to increase with planetary mass, and we suggest that massive terrestrial planets may escape the stagnant-lid regime through the formation of a self-destabilizing dense eclogite layer.